Diesel's street margin is down 33 cents to $1.28 a gallon

The retail-wholesale spread on diesel is $1.28 now, 33 cents thinner than it was 30 days ago. Every gallon moving at the same volume as last month carries 33 cents less gross margin than it did. Retail diesel is $4.578, down 12.1 percent for the month, and it is sitting at the 51 percent mark of its 30-day range. Street price came down, and wholesale did not follow it all the way.

Crude fell faster than product

The reason shows up upstream. WTI is off 16.4 percent in 30 days and it is at the 12 percent mark of its 30-day range. Brent is at the 15 percent mark. Crude has retraced most of the month's move while gasoline at $3.911 is still at the 58 percent mark of its own range and diesel is at 51. Product prices are holding up better than the crude behind them. The 3:2:1 crack spread is $59.14, wider by $13.16 over the same 30 days. The wider crack suggests refiners are capturing cheap crude against product that has not fully repriced.

What that leaves at the rack

The marketer absorbs the difference between rack and street. Rack has stayed firm on the strength of that crack, and retail has come off with the headline crude number that customers read about. The spread gave up 33 cents over the month.

Watch whether the crack holds near $59. A spread that wide usually invites more runs, and if refiners push volume into a market where crude is already near the low end of its range, rack could soften and give some of that 33 cents back to the street. It may take a few weeks to show up in your margin, and it may not show up at all if crude turns.